Permanently radially compressed column

ABSTRACT

A permanently radially compressed chromatographic column having a flexible-walled encasement containing chromatographic media, and a wound element surrounding the encasement for radially compressing the column.

FIELD OF THE INVENTION

The present invention relates generally to high performance liquidchromatography (HPLC), and more specifically to HPLC columns.

BACKGROUND OF THE INVENTION

Chromatography is a method by which components of a solution phase areseparated by the different affinities exhibited by the components for astationary phase. Chromatography has become an important tool formeasuring the compositions of materials used in the chemical,pharmaceutical, biotechnological, and food industries.

HPLC instrument is comprised of a pump for delivering and movingsolvents (the mobile phase), an injector to introduce a sample ofinterest into the flow of the mobile phase, a tubular column encasement,containing a packed material or bed (the "stationary phase"), and adetector to register the presence and amount of different components inthe mobile phase. When the mobile phase is passed through the stationaryphase, each component will emerge from the column at a different timebecause different component in the sample will have different affinitiesfor the packing material. The presence of a particular component in themobile phase exiting the column can be detected by measuring changes inphysical or chemical properties of the eluent. By plotting thedetector's signal over time, response "peaks" corresponding to thepresence of each of the components of the sample can be observed andrecorded.

The resolution between response peaks in a chromatographic analysis or"run" depends, in part, on providing a uniform and reproducible flow ofthe mobile phase through the stationary phase. Irregularities or changesin the packing material in the column from run to run adversely affectreproducibility of runs, and the reliability of the chromatographicanalysis. For example, voids in the packed bed create flowirregularities, leading to overlapping responses or muted responsepeaks.

The chromatography column encasement is typically stainless steel. Thisencasement is tightly packed with the stationary phase material byslurry packing, by tapping, or by mechanical ramming.

Within rigid-wall steel columns, voids can occur not only within thepacking, but also at the interface between the packing and theencasement wall. This leads to a phenomenon referred to as side or wallchanneling, where the mobile phase travels down the wall of the columneffectively bypassing the packing or stationary phase. Such sidechanneling decreases the reliability and reproducibility of thechromatographic peaks, and hence their analytical value.

While a tightly packed bed is less prone to deterioration, degradationstill occurs no matter how well the packing is initially done. Vibrationduring shipping and handling, temperature fluctuations, and/or mobilephase changes can also cause the formation of voids.

Columns have been made with a plastic encasement containing the packingmaterials. However, such plastic columns tend to have poor performance.Under the pressure of a mobile phase, the plastic expands and voids areformed between the packing material and the plastic tube wall resultingin the loss of performance.

A typical plastic column is packed such that the chromatographic mediumis under initial radial compression. This radial compression is providedby the plastic walls of the column. When used, the column is furtherradially compressed under the influence of gas or liquid. To achievethis the column is placed in a pressure vessel and subjected to externalcompression pressures up to 1000 psi. This approach requires thechromatography bench to be equipped with an appropriately sizedapparatus to provide compression of the column. Such apparatus adds tothe expense of the standard chromatography work station.

A simple mechanism to impart and maintain radial compression onchromatography columns is desired.

SUMMARY OF THE INVENTION

The present invention provides a substantially permanently radiallycompressed chromatography column which does not require additionalcompression on the chromatography bench.

According to the invention, a substantially permanently radiallycompressed chromatographic column is provided having a flexible-walledencasement containing chromatographic media. A wound element is fixedlydisposed surrounding the encasement and provides radial compression ofthe column.

A preferred wound element comprises a wire or filament. The wire orfilament is wound or spun on the encasement under tension. The tensionis translated mechanically as a radially directed compression force.

In the alternative, the wound element is a high tensile tape secured byadhesive means or heat welding to the encasement or the tape itself. Thehigh tensile tape is wound or spun on the encasement under tension. Thetension is translated mechanically as a radially directed compressionforce.

The present invention features increased radial compression. Inaddition, the natural resiliency of the flexible walls of the encasementprevents the formation of voids during handling and shipping. Thepresent invention advantageously provides for permanent radialcompression, such that channeling and other factors which lead toperformance degradation during the use of the chromatography apparatusare substantially diminished.

The present invention also advantageously provides for a low costalternative to the prior art, dispensing with the need for expensiveradial compression apparatus on the chromatography bench.

Further advantageously, the present invention provides a chromatographiccolumn with an enhanced usable life span compared with the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features and advantages of the presentinnovation will be more fully understood from the following detaileddescription of an illustrative embodiment, taken in conjunction with theaccompanying drawing in which:

FIG. 1a depicts one aspect of a column according to the presentinvention;

FIG. 1b depicts the column of FIG. 1a in partial cross-section;

FIG. 2a depicts a further aspect of a column according to the presentinvention; and,

FIG. 2b depicts the column of FIG. 2b in partial cross section.

DETAILED DESCRIPTION OF AN ILLUSTRATIVE EMBODIMENT

The present invention will be described herein with reference to anillustrative embodiment of a permanently radially compressedchromatographic column.

FIGS. 1a and 1b depict one aspect of a chromatographic column accordingto the present invention. As illustrated, the chromatographic column,generally designated by the numeral 50, comprises the following majorparts: a column encasement 52, a wound element in the form of a wire orfilament 54, and a stationary phase 56.

Encasement 52 is a plastic tube having an exterior wall 52a and interiorwall 52b. The interior wall 52b defines a chamber for containing apacking material 56. Encasement 52 is packed with the stationary phase56 as seen in FIG. 1b. The packing of stationary phase 56 forces thewalls of encasement 52 radially outward.

For purposes of clarity and convenience this discussion will refer tothe wound element as a wire 54 with the understanding that a filamentmay substitute for such wire. Wire 54 is wound, under tension, aboutencasement 52. This tension is mechanically translated as a radicalcompressive force. Wire 54 may be wound as one or more layers, as bestseen in FIG. 1b. These layers may run in the same direction or form acrossing pattern. A crossing pattern may be preferred to allow greatertension to be applied to the wire without such wire slipping intogrooves formed by preceding layers. In the alternative, a wrap of tape(not shown) can be placed between layers. Multiple layers allow greatercompressive forces to be placed on the encasement 52.

Preferably, the ends of the wire 54 are be welded, glued or otherwisesecured. Preferably, the initial end of the wrapped wire is secured tothe encasement 52. The end of the wire 54, after the column shell 52 hasbeen wound, is secured to the encasement 52 or preceding layers orwindings of the wire.

Wire is readily available from a variety of vendors. A filament of hightensile plastic may be substituted for wire 54. Filaments are availablefrom several vendors. Such filaments are commonly employed for fish lineand the like. Smaller diameter filaments are widely used by industry formanufacturing various vessels.

FIG. 2a depicts a further aspect of a chromatographic column accordingto the present invention. As illustrated, the chromatographic column,generally designated by the numeral 60, comprises the following majorparts: a column encasement 52, a wound element in the form of a hightensile tape 64, a packing medium 56. Encasement 52 is a plastic tubehaving an exterior wall 52a and an interior wall 52b. The interior wall52b defines a chamber for containing a packing material 56. Encasement52 is packed with the stationary 56, as seen in FIG. 1b. The packing ofstationary phase 56 forces the walls of encasement 52 radially outward.

High tensile tape 64 is wound, under tension, about encasement 52. Thistension is mechanically translated into a radial compressive force. Hightensile tape 64 is wound as a single sheet comprising one or morelayers, as tape is carried on a tape dispenser; or, as multiple sheetscomprising one or more layers as illustrated in FIG. 2b. These sheetsmay run in the same direction or form a crossing pattern. Preferably,the high tensile tape 64 has no folds and lies substantially flatagainst the surface of the encasement 52. Multiple layers allow greatercompressive forces to be placed on the encasement 52.

Preferably, the high tensile tape 64 has an adhesive surface to adhereto the encasement 52 and to layers of tape. In the alternative the endsof the tape may be heat welded, glued or otherwise secured.

High tensile tape is readily available from a variety of vendors. Hightensile tape is commonly employed to seal and secure packages and mail.High tensile tape may further comprise filaments and webbing. Onesuitable high tensile tape is sold as packing tape.

Preferably, encasement 52 has packing medium 56 in place and underpressure as the wire 54 or high tensile tape 64 is wrapped. The securedends of the wire 54 or tape 64 prevent the wire or tape from unwindingand releasing the radial pressure, particularly as the internal pressureof the column increases during the flow of a mobile phase through thecolumn 50 or 60.

The column 50 or 60 may be equipped with seals and fittings known in theart. These seals and fittings allow the column to be placed in fluidcommunication with pumps and detectors. Seals and fittings are describedin a copending U.S. patent application Ser. No. 09/079,994, filed May15, 1998, entitled "Permanently Compressed Chromatography Cartridge".

A further embodiment of the present invention comprises a method ofmaking a chromatographic column. The method comprises the steps ofproviding a encasement 52. The method further comprises the step ofwrapping a wound element 54 or 64 around the encasement 52. Andpreferably the method comprises the stage of securing the wound element54 or 64 to the encasement 52 to itself.

Preferably, the encasement 52 contains a chromatographic media 56 whichmedia is radially compressed with the encasement 52. In the alternative,the method comprises the step of placing a chromatographic media in theencasement 52 after such encasement is wrapped with a wound element 54or 64.

The present invention advantageously supplements the natural resiliencyof the flexible walls of a encasement with that of a wound element thusmaintaining the encasement under increased radial compression. Thisoffers distinct advantages over metal columns, which cannot becompressed and also over the prior art flexible wall columns. Thepresent invention, by permanently radially compressing the columns withforces sufficient to maintain uniformity of the separation mediumdispenses with numerous problems inherent in the prior art design.

Further, the present invention can be manufactured inexpensively. Use isnot required complicated apparatus for radially compressing the columncomposed of a source of pressure, a chamber, tubing, check valve(s),gauge(s), etc. is replaced by a simple device that holds the columnbetween two end connectors.

Although the invention has been shown and described with respect toexemplary embodiments thereof, various other changes, additions andomissions in the form and detail thereof may be made therein withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. A permanently radially compressed chromatographiccolumn comprising: a flexible-walled encasement having a cylindricalexterior wall and a cylindrical interior wall, said interior walldefining a chamber for containing chromatographic media; chromatographicmedia held within said chamber; and, a wound element surrounding theencasement upon said exterior wall to radial compress the encasementsaid wound element being selected from the group consisting of wire,filament, and tape.
 2. The permanently radially compressedchromatographic column of claim 1, wherein said wound elementsurrounding the encasement comprises a wire or filament.
 3. Thepermanently radially compressed chromatographic column of claim 1,wherein said wound element is a tape.
 4. The permanently radiallycompressed chromatographic column of claim 3, wherein said tape is hightensile tape.
 5. The permanently radially compressed chromatographiccolumn of claim 3, wherein said tape forms layers.
 6. The permanentlyradially compressed chromatographic column of claim 5, wherein saidwound element wrapped around the encasement under tension to provide aradical compressive force on the encasement.
 7. The permanently radiallycompressed chromatographic column of claim 1, wherein said wire orfilament is wound in layers.